Operations of spinal conditions occurring in the area of the lumbar or thoracic vertebral column may be carried out using an anterior approach. Such an approach may be beneficial because pathological processes often affect the anterior column of the spine. Access to the spinal cord also may be easier to achieve via anterior rather than posterior surgical approaches. Additionally, decompressing the spinal cord may be accomplished more simply or effectively by using an anterior approach. The mechanics of supporting the anterior column may also provide a superior alternative to posterial lateral fixation or fusion. Further, as fewer muscular, neurological and vascular structures may be damaged during spinal surgery using an anterior technique—as compared to a posterior approach—patients can benefit from fewer complications and enjoy faster recovery due to less trauma surrounding the surgical site. Accordingly, new and innovative techniques for treating the spine via anterior approach techniques are being developed.
One internal anterior fixation system for the treatment of vertebral burst fractures known from the related art is disclosed in WO 94/06360 to Danek. This fixation system includes an elongated plate having integral superior, inferior and bridge portions. The superior and inferior portions are provided for fixation to corresponding vertebrae with the bridge portion spanning between the portions over the affected vertebra. The superior portion includes a pair of generally parallel elongated slots, each having scallops for receiving bone fixation screws or bolts. The inferior portion includes a pair of openings through which fixation screws or bolts extend. The slots in the superior portion allow for compression or distraction of the intermediate vertebral region. The openings in the inferior portion are oriented at an oblique angle relative to the longitudinal axis of the plate to provide a quadrilateral fixation construct. The bridge portion has a width significantly less than the width of the superior and inferior fixation portions. In certain embodiments of this known fixation system, the two posterior bone screws may be inserted prior to the implantation of the bone plate. After the insertion of the two bone screws, the bone plate is introduced into the patient's body through a small incision, placed onto the bone screws, and fastened thereon by means of nuts. Once the bone plate has been fixated, the two anterior screws are screwed into the bone plate through corresponding screw holes.
Another fixation system for vertebral bodies which permits contraction or distraction of parts to be connected during an operation is known from EP 0 829 240 to Harms. This known bone plate comprises a first portion having an elongated hole, extending in the longitudinal direction of the intermediate portion and a second portion having bores, and being connectable with the first portion. A screw connecting the two portions is provided and guided through the elongated hole, for connecting the two portions. One of the portions comprises a structured surface, and the other portion comprises a recess for registering therewith. A fixating element is provided for engagement with the structure for locking the relative position of the two portions relative to each other. Due to the elongate holes, the overall length of the plate is variably adjustable.
Additionally, U.S. Pat. No. 5,707,372 discloses a variable length cross-link device which may be affixed to the rods of a dual rod implant apparatus, or to the heads of opposing pedicle screws through which such rods are positioned. The device is capable of assuming variable length and a variable angulation.
Also, U.S. Pat. No. 5,470,333 discloses a system for stabilizing the cervical and the lumbar region of the spine with an anatomically correct curvature.
Despite these developments, a need exists for an anterior fixation system for vertebral bodies that allows manipulation of the vertebrae for correcting malpositions, which includes the possibility of length adjustment over a long distance, and which permits lordosis and kyphosis formation in vivo even after the implant has been placed.